The present invention relates to circuits for operating a plurality of bi-directional motors and, more particularly, to circuits for operating a plurality of bi-directional motors with a system voltage greater than a motor operating voltage.
Prior art circuits for operating a plurality of bi-directional motors have included a H-shaped full bridge driver for each motor. In this type of circuit design, each H-shaped full bridge driver, often referred to as a H-bridge driver, is controlled by a microprocessor to operate the respective motor in either the forward or reverse direction independent of the other motors.
Each H-bridge driver requires four electrical switching components, such as transistors or relays. Thus, a prior art control circuit for operating four bi-directional motors requires sixteen switching components. The addition of each switching component to a control circuit decreases the reliability of the control circuit and increases the cost of the control circuit. Further, each switching component requires a separate microprocessor control port increasing the cost of the microprocessor.
The present invention provides a circuit for operating a plurality of bi-directional motors, each motor having a pair of terminals disposed across the motor. The circuit includes a common half bridge for providing one of power and ground to one of the pair of terminals across each motor. A plurality of particular or individual half bridges, one particular half bridge for each motor, provide the other of power and ground to the other of the pair of terminals across each motor. A controller selectively controls the common half bridge and the particular half bridges to supply power in either direction across the pair of terminals of one or more of the motors.
In a preferred embodiment, the controller selectively controls the common half bridge and the particular half bridges to independently pulse width modulate power in either direction across the pair of terminals of one or more of the motors. To simultaneously operate two or more motors in the same direction or opposite directions, the controller selectively controls the common half bridge and the particular half bridges to energize the two or more motors in a sequential or random order.
The present invention provides particular advantages when utilized in an electrical system providing a system voltage greater than a motor operating voltage, e.g. in a vehicle having an electrical system providing a forty-two volt system voltage to operate twelve volt motors. With the system voltage being greater than the motor operating voltage, power can be pulsed or pulse width modulated independently to each motor. By pulse width modulating the system voltage at the appropriate duty cycle, all motors can be operated simultaneously or concurrently at full power with each individual motor being driven in a direction independent of the other motors. The duty cycle of the pulse width modulation can be varied to (1) increase power to and thereby increase the speed of a selected motor if, for example, the motor is stalled, or (2) decrease power to and thereby decrease the speed of selected motors if, for example, the electrical system is overloaded. The circuit can shed loads (i.e. stop powering or energizing selected motors if the electrical system is overloaded). When a reduced amount of supply power or system voltage is available, the circuit can share the reduced amount of power or voltage among loads (i.e. operate the motors at a reduced speed or power).